At the time this specification was prepared, the technical standard for transferring large-scale data in a wireless home network was being developed by one of the task groups of IEEE 802.15.3c. This standard defines the use of an electric wave having a physical wavelength in the millimeter range for large-scale data transfer (mmWave). In general, this frequency band is an unlicensed band and has been limited to communication service providers, radio astronomy, vehicle collision prevention, and the like.
In IEEE 802.11b or IEEE 802.11g, the carrier frequency is 2.4 GHz and the channel bandwidth is about 20 MHz. In IEEE 802.11a or IEEE 802.11n, the carrier frequency is 5 GHz and the channel bandwidth is about 20 MHz. In contrast, the mmWave standard calls for a carrier frequency of 60 GHz and a channel bandwidth of about 0.5˜2.5 GHz. Therefore, the mmWave has a carrier frequency and channel bandwidth considerably greater than those used in the other conventional IEEE 802.11 standards. If a radio frequency signal having a wavelength in the millimeter range is used, it is possible to provide a considerably high data rate on the order of several gigabits (Gbps). It is also possible to implement this using a single chip including an antenna having a size of 1.5 mm or less.
Because the attenuation ratio of air is very high, it is advantageous to reduce inter-station interference. Likewise, in the case of mmWave transmissions, the reaching (i.e., maximum) distance of beam is also decreased due to the high attenuation ratio. Therefore, it is particularly difficult to transmit a signal omni-directionally. In order to solve this problem, a beam needs to be sharpened. In so doing, the beam is locally delivered only (i.e., is limited to a relatively small coverage area).
Because the reaching distance is significantly limited due to the high attenuation ratio and as a result the beam is typically sharpened, another problem arises, that is, communication is not normally performed in a non-line-of-sight environment. Typically, mmWave based systems solves the former problem by using an array antenna having a high gain. Further, mmWave based systems solve the latter problem by using beam steering.
When transmission loss is considerable, in case that limitation is put on transmission power, it is able to secure a specific propagation distance by obtaining an antenna gain using antenna technology. For this, a method of forming and maintaining a beam link is required.
FIG. 1 is a block diagram of an exemplary radio network to which the present invention applies. The network includes a main station that manages all of the beam links operating in the network. The beam links provide directional communication. As such, these are illustrated in FIG. 1 as ovals.
FIG. 1 shows that certain beam links between two stations are compatible with respect to neighboring stations. Compatibility is determined by checking whether neighboring stations will have a problem with a given beam link. Other beam links, such as beam links 110, 120 and 130 are illustrated as having compatibility problems with one or more neighboring stations. This is indicated by the ‘X’.
In order to determine whether a beam link is compatible, all of the stations A to F must check whether the beam link will be compatible and then deliver the check results to the main station.